Wiring diagram for second gen W126 door locking vacuum pump

[cmac2012]

Anybody have that? In the old days, I would get some help with wiring diagrams from the Haynes manuals - apparently they didn't think there was enough DIY interest in the W126 to justify creating one.

Somewhere I have in my stuff a Haynes manual that covered the OM603 in the W124 not sure if it would have what I'm looking for.

I'm trying to connect an aftermarket keyless locking system to my '86 300SDL. It's hard slogging.

Their instructions tell me to find the NO, NC, and common leads. Five wires come back to the pump, a hot, a ground, and three wires in a bundle: blue, yellow and green. A second bundle of blue, yellow and green also are involved, I don't quite get it.

My understanding of a normally closed (NC) circuit is one with 12 volts while the system is at rest. I connected a wire to a jumper cable going to the negative battery terminal, sliced a little bit of the insulation off the blue, yellow and green wires, and each one of them reads battery voltage. Wouldn't a NO (normally open) lead show 0 V when touched to ground? And I'm not real sure what the definition of a common lead is. I've read a few things about it, but I'm still in the dark.

[Frank Reiner]

cmac:

There are two wiring diagrams for the '86 model year; they differ only on the power supply portion of the wiring. What is your date of manufacture?
The power supply plug on the pump has three wires: brown, black/yellow, and red/white.
The control wiring is in the other plug: blue, yellow, and green. Blue goes to the left front door actuator, yellow to the right front, and green to the trunk.

[cmac2012]

I appreciate all of that, but it doesn't get at my problem. I need to know how to connect the wires to the little wiring hub that came with the unit. I've read that sometimes the wiring diagrams will indicate which leads are normally closed, normally open, or common. Apparently that's the information I need. It appears to me that all three of the control wires - the green, yellow and blue - are normally closed

Their instructions are possibly helpful, but I can't make out what to do with them:





It comes with numerous other alleged features which I am not interested in.

The trunk lock no longer responds to a key.

One of the main reasons I want to hook this up is to have a quick way to lock the trunk. Right now, the locking feature works. If I lock one of the front doors with the key everything including the trunk locks.

Last thing I want do is accidentally wire this up wrong and fry something in the vacuum unit.

[Frank Reiner]

To refer to the instructions with the phrase "Through a Glass, Darkly" would be generous. They are damn near opaque.
You are correct about the three wires (blue, yellow,green) all being positive (when the doors and trunk are unlocked). In the rest (unlocked) position each door switch is connected to positive. When the key is turned in the locking direction (clockwise) the respective trigger wire is disconnected from power and grounded. A positive voltage on the signal wire causes the pump to supply pressure, and a negative voltage on the signal wire causes the pump to reverse rotation and supply vacuum. The locking or unlocking signal can come from any of the three actuators; the other two will then be moved to the corresponding position pneumatically, and the switch contacts will confirm to the pump controller that they are locked (or unlocked). It does not appear that the remote unit is capable of performing that function.

[Frank Reiner]

cmac:

It may be possible to wire the device thus:
Yellow to positive (+).
Orange to ground (-).
White to the blue signal wire of the pump harness.
The drawings for the device would indicate that the white com terminal can be alternately connected to either yellow or orange. The question is whether the switch remains latched to either yellow or orange once connected, or if one of those two is a momentary connection.

This will create a second "door switch" in parallel with the left front switch.

With all that said, would it not be easier to figure out why the key will not mechanically operate the trunk lock? Since the trunk lock does operate via the electrical/pneumatic actuator, it seems likely that the mechanical problem lies in the linkage between the key cylinder and the actuator.